Officials have not confirmed the nationalities or identities of the soldiers, but BBC correspondent Quentin Sommerville in Kabul said that US troops were operating in the area.Witnesses said the attacker, who rode a motorcycle laden with explosives towards a patrol, waited for the troops to get out of their vehicle before detonating the bomb, which also killed at least six civilians.Taliban insurgents have admitted to carrying out the attack, which also killed four Afghan police and injured 60 people.The Taliban Islamists said on their website that the attack was carried out by ‘a hero mujahid, Shohaib, from Kunduz’, before claiming that eight foreigners and six Afghan soldiers were killed.

Khost has seen a dramatic rise in violence in recent months, with a similar attack in June killing 21 people, including three US soldiers and a local interpreter.

Nato currently has more than 100,000 troops fighting Taliban insurgency in Afghanistan, but they are due to pull out by the end of 2014.

Over the weekend, a shooting at a checkpoint in eastern Afghanistan, during which three US troops and a contractor were killed, took the US military’s death toll in the war past 2,000.